Cable operated rotary temperature control devices are presently available for controlling opening and closing of a vent or the like in a HVAC unit. These devices typically comprise an output pulley and an input pulley with a cable wrapped around them to impart rotary movement to a vent door or the like connected to the output pulley. The input pulley rotates the output pulley and hence controls any unit connected thereto. Such cable operated control devices need a mechanism for taking up slack to effectively control the unit connected to the output pulley. In this regard, U.S. Pat. No. 4,936,159 issued to Kallio and 5,129,281 and 5,301,563 issued to Van Zanten et al, and 5,235,866 issued to Truman, et al. disclose cable operated rotary temperature control devices.
The '866 patent, assigned to the assignee of the present application, discloses a rotary temperature device having input and output pulleys connected by a cable and a spring mechanism connected between the output pulley and the cable for initially taking up slack in the system. The disclosure of the '866 patent is incorporated herein by reference.
The '159 patent also discloses a rotary control device with a spring on one or both ends of the cable and positioned in holes formed in the output pulley.
The '281 patent discloses a rotary control device with a slack adjustment mechanism which, in turn, includes an adjustable spring mechanism at each end of the cable and a plurality of cooperating ratchet-like stops formed within the output pulley. A movable retainer member holds each end of the cable relative to the output pulley in any of a number of adjusted positions. The slack in the cable is thereby adjusted by pushing the retainer member away from the spring, with the ratchet-like stops maintaining the retainer member in position.
The '563 patent discloses a number of slack adjustment mechanisms formed within the output pulley. These mechanisms operate in a manner similar to the constructions of the '281 patent to adjust the amount of slack in the system.
In all of the devices discussed above, the spring is contained entirely within the output pulley and can only provide limited slack control. This is because of the constraints imposed on the slack control mechanism due to the shape and size of the output pulley and housing. Without unduly enlarging the size of the output pulley and housing, any spring mechanism used for taking up initial slack or for adjusting the slack in the system must be small in size. This, in turn, permits only a limited amount of spring movement. The inclusion of the spring mechanism on the output pulley also takes up space which might otherwise be used for other control mechanisms.